The present invention relates to robots and more particularly to the manner in which robot acceleration and deceleration motion is controlled.
In the application of robots, the user often writes programs that direct the robot to move the tool tip to a series of points and/or through a series of path segments and perform defined tasks at the points or along the paths. Each path segment may involve motion for each joint that includes acceleration for a specified time to a slew (constant) velocity, operation at slew velocity for a specified time, and deceleration for a specified time to rest. Coordination of the motion of the joints results in the desired tool tip motion.
The robot control typically has a single scheme for accelerating or decelerating the robot joints when speed changes are directed by the robot program. Thus, the user may program acceleration/deceleration rates but normally has little or no freedom in specifying the character (referred to as the profile) of the acceleration or deceleration.
The acceleration/deceleration profile accordingly has typically been built into the robot control, i.e. the user specifies when and at what rate acceleration/deceleration is to occur and the typical prior art robot control executes the motion with its fixed acceleation/deceleration profile. The acceleration profile, for example, may be a squarewave which results in a trapezoidal velocity profile. Among other possible acceleration profiles, sinusoidal profiles have been proposed in technical papers and if implemented would result in a sinusoidal velocity profile.
Generally, prior art schemes are satisfactory, but since the character of acceleration/deceleration in segments of robot arm motion affects the smoothness, accuracy, and speed of tool tip motion there have been limitations on the quality with which robot motion can be produced. For example, a profile employed to reach slew speed rapidly may cause overshoot on deceleration. As another example, a profile that provides smooth motion over one motion segment may provide unduly slow motion over another motion segment.
Since various acceleration/deceleration profiles can be employed to achieve different objectives in robot control, it is desirable that greater freedom be provided in prescribing acceleration/deceleration motion for robots. The present invention is directed to a robot control that achieves this end. Its implementation is facilitated by the completely digital character of the robot control disclosed in the referenced patent applications.